Polyvinyl chloride (PVC) and chlorinated PVC (CPVC) can be foamed to provide lighter, less expensive articles. It is important that the PVC foams fuse quickly to allow for sufficient melt strength for foaming. PVC and CPVC foams can be developed via physical blowing agents or chemical blowing agents. Process aids are typically used to provide melt strength. Process aids can also facilitate the fusing process. Acrylic copolymer fusion aids that have at 80 weight percent and greater methylmethacrylate units have been used.
US 2009111915 by Applicant describes an improved acrylic copolymer for use in highly filled PVC flooring, pipe and siding. The copolymer has a lower MMA content, and a lower Tg than previously used acrylic copolymers
There is a desire to produce PVC foams at lower operating temperatures. Lower operating temperatures save energy costs, improve product appearance, and also provide a safer working environment.
Applicant has surprisingly discovered that the use of an acrylic copolymer process aid with a lower level of methyl methacrylate monomer units than currently used can effectively used in PVC foam manufacture, providing the same level of fusion at lower temperatures, or a higher level of fusion at the same temperature, when compared to the acrylic copolymer process aids currently used having higher Tgs. A decreased processing temperature of up to 10° C., with the same level of fusion, have been seen using the improved acrylic copolymer of the invention. Further, lower operating temperatures allow for faster downstream cooling, offering potentially faster production speeds and improved product quality/appearance due to less heat history of the polymer.